How I used GIMP to process my astronomical sketches 26/5/14
Open original image in GIMP
Rotate it to correct orientation
Invert colours
Chose selection tool
Select object by taking mouse to start point, pressing and holding down left mouse button whilst drawing around object until get back to start point
Use Gaussian blur to turn lines into smudges – choose settings to reflect look you want
Result of Gaussian Blur
Whilst still having selected the object, now use levels and brightness/contrast to adjust look Selecting levels (left), and initial levels setting (below) Levels setting after adjustment (left)
Saving final image
Final result